Concentrated solar power (CSP) collectors have been increasingly used in recent times in conjunction with thermal storage media such as molten salts in order to maximize the conversion of solar energy collected into usable mechanical work. For example salt-based thermal storage media have been used in large-scale solar-thermal power projects to extend power output to periods when the sun is not shining. Existing solar collectors use parabolic mirrors, dish shaped mirrors, Fresnel lenses, and other lens and mirror configurations to focus solar energy on flat panel or evacuated tube collectors, which in turn provide heat to a thermal storage medium or heat exchanger.
Evacuated tube and flat panel collectors usually work by using the collected solar energy from parabolic, dish, flat panel or linear Fresnel collectors to heat an absorption medium that then heats a heat transfer fluid such as molten salts or anti-freeze chemicals such as propylene glycol, and this fluid is then used to heat a thermal storage medium or to generate steam or other hot gases via a heat exchanger. While this approach accommodates high temperatures in the heat transfer fluid, in the range of 300-400 degrees Celsius, the thermal storage media, often phase change materials such as nitrate salts and other molten salt mixtures, can directly absorb much higher temperatures without boiling. However, most existing solar collectors such as parabolic or flat panel collectors are not configured to produce higher heating temperatures, and utilize heat transfer fluids to transfer heat to the thermal storage media, likely due to the difficulty of absorbing temperatures that could damage existing flat panel or evacuated tube collectors and to difficulties in pumping thermal storage media. For example, parabolic collectors focus the incident solar radiation across only a single spatial dimension onto long evacuated tube collectors, resulting in radiative, convective, and other thermal losses across the large area of the collector surface. Projects using molten salts as heat transfer fluids also suffer from challenges resulting from the high freezing temperature of the salt media and the resulting damage to piping system. Current projects that use solar radiation to directly heat the thermal storage media at a central point of absorption, such as solar tower projects utilizing salt storage media, currently focus the solar radiation via large heliostat mirrors, thus posing a danger to passersby and birds and losing a great deal of energy to reflection back into the environment and to inefficiencies in mirror technology. This method also suffers from so-called “cosine losses” resulting from imperfect focusing of the solar radiation on the central absorber tower.